Image-processing apparatus, an image-forming apparatus, and a program

• US 20090207453A1
• Filed: 10/27/2005
• Published: 08/20/2009
• Est. Priority Date: 10/29/2004
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Hirano, Masanori, Ike, Takahiro
• Granted Patent: US 7,660,016 B2
• Time in Patent Office: Days
• US Class Current: 358/3.220
• CPC Class Codes: H04N 1/40087 Multi-toning, i.e. converting a continuous-tone signal for reproduction with more than two discrete brightnesses or optical densities, e.g. dots of grey and black inks on white paper

Abstract

An image-processing apparatus for quantizing multi-level (M-level) image data into N-level values, where M>N>1, using a multi-level error-diffusion process or a minimum-average multi-level error method is disclosed.

The image-processing apparatus includes: means for outputting correction data; means for setting a quantization-threshold value; means for comparing the correction data and the quantization-threshold value so as to output N-level image data; and means for calculating an error generated with generating the N-level image data.

Claims

1. An image-processing apparatus for quantizing multi-level (M-level) image data into N values, where M>

N>

1, using a multi-level error-diffusion process or a minimum-average multi-level error method, comprising;

means for outputting correction data in which an error diffused from already-quantized pixels therearound is added to the multi-level image data of a pixel in question;

means for setting a quantization-threshold value based on the multi-level image data of the pixel in question;

means for comparing the correction data and the quantization-threshold value so as to output N-level image data;

and means for calculating an error generated when generating the N-level image data;

wherein, assuming quantized values are 0, 1, 2, . . . , N-1, and tones of the quantized values are V0, V1, V2, . . . , VN-1, respectively at least one threshold value Th_a+1 in an interval between V_a and V_a+1 (where 0≦

a<

N-1) of at least one input value, when an input tone value is ν

, is set based on equation (1), where the equation (1) is;

Th_a+1=(√

{square root over ( )}((ν

−

V_a)(V_a+1−

V_a)/2)))+V_a.

2. The image-processing apparatus as claimed in claim 1, wherein the threshold value is set based on said equation (1) only when, in the input value interval between V_a and V_a+1 (where 0≦

a<

N-1), the input value ν

is greater than a constant K_a (where V_a<

K_a<

V_a+1).

3. The image-processing apparatus as claimed in claim 1, wherein the threshold value is obtained through a sequential process depending on the input value ν

.

4. The image-processing apparatus as claimed in claim 2, wherein the threshold value is obtained through a sequential process depending on the input value ν

.

5. The image-processing apparatus as claimed in claim 1, wherein the threshold value is obtained from a look-up table depending on the input value ν

.

6. The image-processing apparatus as claimed in claim 2, wherein the threshold value is obtained from a look-up table depending on the input value ν

.

7. An image-forming apparatus for quantizing input multi-level (M-level) image data into N values, where M>

N>

1, using a multi-level error-diffusion process or a minimum-average multi-level error method and forming an image using dots which correspond to each of the N values, comprising;

means for outputting correction data in which an error diffused from already-quantized pixels therearound is added to the multi-level image data of a pixel in question;

means for setting a quantization-threshold value based on the multi-level image data of the pixel in question;

means for comparing the correction data and the quantization-threshold value so as to output N-level image data;

and means for calculating an error generated when generating the N-level image data;

wherein, assuming quantized values are 0, 1, 2, N-1, and tones of the quantized values are V0, V1, V2, . . . , VN-1, respectively at least one threshold value Th_a+1 in an interval between V_a and V_a+1 (where 0≦

a<

N-1) of at least one input value, when an input tone value is ν

, is set based on equation (1), where the equation (1) is;

Th_a+1=(√

{square root over ( )}((ν

−

V_a)(V_a+1−

V_a)/2)))+V_a.

8. The image-forming apparatus as claimed in claim 7, wherein the threshold value is set based on said equation (1) only when, in the input value interval between V_a and V_a+1 (where 0≦

a<

N-1), the input value ν

is greater than a constant K_a (where V_a<

K_a<

V_a+1).

9. The image-forming apparatus as claimed in claim 7, wherein the threshold value is obtained through a sequential process depending on the input value ν

.

10. The image-forming apparatus as claimed in claim 8, wherein the threshold value is obtained through a sequential process depending on the input value ν

.

11. The image-forming apparatus as claimed in claim 7, wherein the threshold value is obtained from a look-up table depending on the input value ν

.

12. The image-forming apparatus as claimed in claim 8, wherein the threshold value is obtained from a look-up table depending on the input value ν

.

13. The image-forming apparatus as claimed in claim 7, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

14. The image-forming apparatus as claimed in claim 8, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

15. The image-forming apparatus as claimed in claim 9, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

16. The image-forming apparatus as claimed in claim 10, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

17. The image-forming apparatus as claimed in claim 11, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

18. The image-forming apparatus as claimed in claim 12, wherein the image is formed with one of an electrophotographic method, an ink-jet method, and a thermal transfer method.

19. A program for causing a computer to execute a process of quantizing multi-level (M-level) image data into N values, where M>

N>

1, using a multi-level error-diffusion process or a minimum-average multi-level error method, comprising;

a code for a step of outputting correction data in which an error diffused from already-quantized pixels therearound is added to the multi-level image data of a pixel in question;

a code for a step of setting a quantization-threshold value based on the multi-level image data of the pixel in question;

a code for a step of comparing the correction data and the quantization-threshold value so as to output N-level image data;

and a code for a step of calculating an error generated when generating the N-level image data,

wherein, assuming quantized values are 0, 1, 2, . . . . N-1, and tones of the quantized values are V0, V1, V2, . . . , VN-1, respectively at least one threshold value Th_a+1 in an interval between V_a and V_a+1 (where 0≦

a<

N-1) of at least one input value, when an input tone value is set to be ν

, is set based on equation (1), where the equation (1) is;

Th_a+1=(√

{square root over ( )}((ν

−

V_a)(V_a+1−

V_a)/2)))+V_a.

20. The program as claimed in claim 19, wherein the threshold value is set based on said equation (1) only when, in the input value interval between V_a and V_a+1 (where 0≦

a<

N-1), the input value ν

is greater than a constant K_a (where V_a<

K_a<

V_a+1).